Lecture #23Base Current Components (Active Bias)Circuit ConfigurationsModes of OperationBJT ElectrostaticsSlide 6BJT Performance Parameters (PNP)Collector Current (PNP)Summary: BJT FundamentalsSlide 10Notation (PNP BJT)Ideal Transistor AnalysisEmitter Region FormulationBase Region FormulationCollector Region FormulationEE130 Lecture 23, Slide 1Spring 2007Lecture #23QUIZ #3 Results (undergraduate scores only, N = 39)Mean = 22.1; Median = 22; Std. Dev. = 1.995High = 25; Low = 18OUTLINE The Bipolar Junction Transistor– Fundamentals– Ideal Transistor AnalysisReading: Chapter 10, 11.1EE130 Lecture 23, Slide 2Spring 2007The base current consists of majority carriers supplied for1. Recombination of injected minority carriers in the base2. Injection of carriers into the emitter3. Reverse saturation current in collector junction•Reduces | IB |4. Recombination in the base-emitter depletion regionBase Current Components (Active Bias)EMITTERBASECOLLECTORp-typen-type p-typeEE130 Lecture 23, Slide 3Spring 2007Circuit ConfigurationsOutput Characteristics for Common-Emitter ConfigurationEE130 Lecture 23, Slide 4Spring 2007Modes of OperationCommon-emitter output characteristics (IC vs. VCE)Mode Emitter Junction Collector JunctionCUTOFF reverse bias reverse biasForward ACTIVE forward bias reverse bias*Reverse ACTIVE reverse bias* forward biasSATURATION forward bias forward bias*or not strongly forward biasedEE130 Lecture 23, Slide 5Spring 2007BJT Electrostatics•Under normal operating conditions, the BJT may be viewed electrostatically as two independent pn junctionsEE130 Lecture 23, Slide 6Spring 2007Electrostatic potential, V(x)Electric field, (x)Charge density, (x)EE130 Lecture 23, Slide 7Spring 2007BJT Performance Parameters (PNP)•Emitter Efficiency:–Decrease (5) relative to (1+2) to increase efficiency•Base Transport Factor:–Decrease (1) relative to (2) to increase transport factorEpCpTIITdc•Common-Base d.c. Current Gain:EnEpEpIIIEE130 Lecture 23, Slide 8Spring 2007Collector Current (PNP)•The collector current is comprised of•Holes injected from emitter, which do not recombine in the base (2) •Reverse saturation current of collector junction (3)where ICB0 is the collector current which flows when IE = 0 000 α1α1ααCEBdcCBBdcdcCCBBCdcCIβIIIIIIII0αCBEdcCIII •Common-Emitter d.c. Current Gain:dcdcBCdcII1EE130 Lecture 23, Slide 9Spring 2007Summary: BJT Fundamentals•Notation & conventions:•Electrostatics:–Under normal operating conditions, the BJT may be viewed electrostatically as two independent pn junctionsIE = IB + ICpnp BJT npn BJTEE130 Lecture 23, Slide 10Spring 2007•Performance parameters:–Emitter efficiency–Base transport factor–Common base d.c. current gain–Common emitter d.c. current gainEnEpEpIIIECpTIIdcdcdcBCdcII1EpCpTIIEE130 Lecture 23, Slide 11Spring 2007Notation (PNP BJT)NE = NAEDE = DNE = nLE = LNnE0 = np0 = ni2/NENB = NDBDB = DPB = pLB = LPpB0 = pn0 = ni2/NBNC = NACDC = DNC = nLC = LNnC0 = np0 = ni2/NCEE130 Lecture 23, Slide 12Spring 2007Ideal Transistor Analysis•Solve the minority-carrier diffusion equation in each quasi-neutral region to obtain excess minority-carrier profiles–different set of boundary conditions for each region•Evaluate minority-carrier diffusion currents at edges of depletion regions•Add hole & electron components together terminal currents0""xdxndEEnEqADI0xdxpdBEpBqADIWxdxpdBCpBqADI0''xdxndCCnCqADIEE130 Lecture 23, Slide 13Spring 2007Emitter Region Formulation•Diffusion equation:•Boundary Conditions:EEEndxndED22"0)1()0"(0)"(/0kTqVEEEEBenxnxnEE130 Lecture 23, Slide 14Spring 2007Base Region Formulation•Diffusion equation:•Boundary Conditions:BBBpdxpdBD220)1()()1()0(/0/0kTqVBBkTqVBBCBEBepWpeppEE130 Lecture 23, Slide 15Spring 2007Collector Region Formulation•Diffusion equation:•Boundary
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